The present invention relates to a treatment system for percutaneous coronary angioplasty or peripheral angioplasty in which a dilation catheter is used to cross a lesion in order to dilate the lesion and restore normal blood flow in the artery. It is particularly useful when the lesion is a calcified lesion in the wall of the artery.
Calcified lesions, currently treated with angioplasty balloons, require high pressures (sometimes as high as 10-15 or even 30 atmospheres) to break the calcified plaque and push it back into the vessel wall. With such pressures comes trauma to the vessel wall which can contribute to vessel rebound, dissection, thrombus formation, and a high level of restenosis. Non-concentric calcified lesions can result in undue stress to the free wall of the vessel when exposed to high pressures. An angioplasty balloon when inflated to high pressures can have a specific maximum diameter to which it will expand but the opening in the vessel under a concentric lesion will typically be much smaller. As the pressure is increased to open the passage way for blood the balloon will be confined to the size of the opening in the calcified lesion (before it is broken open). As the pressure builds a tremendous amount of energy is stored in the balloon until the calcified lesion breaks or cracks. That energy is then released and results in the rapid expansion of the balloon to its maximum dimension and may stress and injure the vessel walls.
Recently, a new system and method has been contemplated for breaking up calcium deposits in, for example, arteries and veins. Such a system is described, for example in U.S. Patent Publication No. 2009/0312768, Published Dec. 17, 2009. Embodiments described therein include a catheter having balloon, such as an angioplasty balloon, at the distal end thereof, arranged to be inflated with a fluid. Disposed within the balloon is a shock wave generator that may take the form of, for example, a pair of electrodes, which are coupled to a high voltage source at the proximal end of the catheter through a connector. When the balloon is placed adjacent a calcified region of a vein or artery and a high voltage pulse is applied across the electrodes, a shock wave is formed that propagates through the fluid and impinges upon the wall of the balloon and the calcified region. Repeated pulses break up the calcium without damaging surrounding soft tissue.
Each high voltage pulse causes an arc to form across the electrodes. The arc in turn causes a steam bubble to form. Each arc results in intense heat and energy for a brief period of time. Inside the small confines of tiny angioplasty balloons the fluid can warm up and become hot enough to damage tissue unless steps are taken to control the amount of energy released into the fluid. Just a two degree Celsius elevation in temperature above body temperature can result in tissue damage.
The amount of energy to assure the formation of the steam bubble and arc can be highly variable from arc to arc. Therefore, if the same amount of energy is used to assure the formation of each bubble and arc, more energy than is necessary will be used to form many of the bubbles and arcs. Excessive heating of the fluid within the balloon may result. Also, because greater applied energies create larger bubbles at the electrodes, the excessive energy will produce a larger bubble than required which can unduly stress the balloon walls.
Another consideration is the amount of energy represented by the high voltage applied to the electrodes. Each high voltage pulse removes a portion of the electrode material. Since the size of the electrodes must be small in order to fit into the calcified vein or artery, they are only capable of sustaining a limited numbers of high voltage pulses sufficient to form the shock wave resulting electrical arc.
Hence, there is a need in the art to be able to control the amount of energy required to produce the bubbles and arcs. It would also be desirable to be able to produce the bubbles and arcs with less energy than hereto for possible. The present invention addresses these and other issues.